Experimental plague in mice, caused by Yersinia pestis, is mediated by two distinct types of virulence factors. Members of the first category serve as whole animal or tissue invasins by promoting dissemination of the organisms into visceral organs following infection by peripheral routes of injection (e.g. intraperitoneal or subcutaneous). Mutants lacking one or more tissue invasins can exhibit significant reduction in virulent (50% lethal dose>102 to 107 bacteria) by peripheral administration but retain essentially full lethality (50% lethal dose ca. 102 bacteria) upon intravenous injection (4). Examples of this group (6, 16, 48) include the outer membrane (46) plasminogen activator (1) mediated by a ca. 10 kb pesticin or Pst plasmid (12, 41) and a series of iron repressible outer membrane peptides (10, 40) encoded by a delectable ca. 100 kb chromosomal segment (11, 22).
Examples of the second category function to promote lethality following infection by the intravenous route, known to facilitate immediate transport of the bacteria to favored niches within visceral organs (4). Mutational loss of these lethal factors causes qualitative (intravenous 50% lethal dose>107 bacteria) decreases in virulence. Included in this group are certain ca. 70 kb low calcium response or Lcr plasmid encoded proteins: V antigen (9, 27), others termed Yops (18, 19, 33, 47): YopE (23, 35, 43, 44, 47), YopH (3, 34, 44), and probably YpkA (13), as well as chromosomally encoded antigen 4 or pH 6 antigen (20) and possibly the murine exotoxin encoded by the ca. 100 kb Tox plasmid (32.). Considerable effort has been spent in study of the regulation, processing, and delivery of these proteins to host cells (2, 15, 26, 28, 30, 31, 35).
The effectiveness of the immune response directed against members of the second category of virulence factors has only been reported for V antigen. Some (17, 24, 27, 39, 49, 50) but not all (5) antibodies directed against this 37 kDa exported (8, 17, 43, 44) protein provided significant passive protection against experimental plague in mice. This effect was associated with release of a potent immunosuppressive block preventing both synthesis of cytokines (27) and formation of protective granulomas (50).
Plague vaccines have been identified in U.S. Pat. No. 3,137,629. The patent describes a process for producing killed plague vaccines which immunizes mice and guinea pigs by growing Pasteurella pestis, killing the strain through mechanical action and solubilizing the extract in strong alkaline solution, and then preparing parenteral vaccine by reducing the pH value of the soluble P. pestis antigenic solution to a neutral pH.
It is an object of the present invention to prepare a plasmid by recombinant techniques.
It is another object of the present invention to prepare an antigen encoded by the recombinant plasmid.
It is a further object of the present invention to control the effect Y. pestis has on mammals by utilizing a vaccine to Y. pestis constituting the antigen noted above.